Organic pigment coating for electronic devices, perovskite solar cells, and methods

ABSTRACT

Methods of passivating a surface. The methods may include providing a mixture including a liquid and a derivative of quinacridone, applying the mixture to a first surface of a film that includes a metal halide perovskite, and annealing the film for a time and a temperature effective to convert the derivative of quinacridone to quinacridone. Composite materials and electronic devices also are provided.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Contract No.FA9550-18-1-0231 awarded by the Air Force Office of Scientific Research,and Contract No. 1709116 awarded by the National Science Foundation. Thegovernment has certain rights in this invention.

BACKGROUND

Perovskite solar cells (PSCs) have benefited from materials developmentand device engineering. During the last decade, power conversionefficiencies (PCEs) have improved from around 4% to more than 25% forsingle junction devices.

However, long-term stability is one of the challenges that hinders thelarge scale commercialization of PSCs. Many approaches have beendeveloped for improving the stability of PSCs, including surfacepassivation of halide perovskite thin films using various types ofmaterials, such as organic halide salts, polymers, organic smallmolecules, low-dimensional perovskite hybrids, and inorganic compounds.

The function of surface passivation is twofold. The first is insuppressing charge recombination at the interfaces between perovskiteand charge transport layers. The second is in increasing devicestability by preventing the penetration of degrading agents (i.e., H₂Oand O₂) into the perovskite layer. While various types of materials havebeen developed as surface passivation agents, the long-term stabilityrequirements for the commercialization of PSCs has not been met by thesematerials.

Industrial organic pigments typically are insoluble organic compounds ofhigh sunshine-resistant coloring strength. Industrial organic pigmentsusually have very low solubilities in water.

There remains a need for improved passivation agents, includingpassivation agents that are easy to process, low cost, stable, or acombination thereof. There also remains a need for improved methods forsurface passivation.

BRIEF SUMMARY

Provided herein are composite materials, electronic devices, and methodsof passivating a surface, such as a surface of a metal halideperovskite, that may be at least partially coated (e.g., passivated)with quinacridone. In some embodiments, surface passivation of halideperovskite thin films with quinacridone is achieved via a facilespin-coating-annealing process, which, as described herein, may resultin highly efficient and/or stable perovskite-based solar cells.

In one aspect, methods of passivating surfaces are provided. In someembodiments, the methods include providing a mixture that includes aliquid and a derivative of quinacridone, wherein the derivative ofquinacridone is at least partially dissolved in the liquid; applying themixture to a first surface of a film, wherein the film includes a metalhalide perovskite; and annealing the film for a time and a temperatureeffective to convert the derivative of quinacridone to quinacridone.

In another aspect, composite materials are provided. In someembodiments, the composite materials include a film that includes ametal halide perovskite, the film having a first side and a second sideopposite the first side; and a coating that includes quinacridone,wherein the coating at least partially coats the first side of the film.

In a still further aspect, electronic devices are provided. In someembodiments, the electronic devices include an electrode, a compositematerial as described herein; and a counter electrode, wherein thecomposite material is arranged between the electrode and the counterelectrode. In some embodiments, the electronic devices also include acharge transport layer arranged between the composite material and thecounter electrode. The electrode may contact the second side of thecomposite material, and the charge transport layer may contact thecounter electrode and the coating including quinacridone. The electronicdevices may include solar cells.

Additional aspects will be set forth in part in the description whichfollows, and in part will be obvious from the description, or may belearned by practice of the aspects described herein. The advantagesdescribed herein may be realized and attained by means of the elementsand combinations particularly pointed out in the appended claims. It isto be understood that both the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a schematic of an embodiment of a layer arrangement foran electronic device.

FIG. 2 depicts a schematic of an embodiment for preparing a quinacridonepassivated perovskite thin film.

FIG. 3 depicts a schematic of a cross-section scanning electronmicroscope (SEM) image of an embodiment of a planar n-i-p PSC includinga quinacridone passivated methyl ammonium lead iodide (MAPbI₃) layer.

FIG. 4 depicts the relative band-edges of stacked films in an embodimentof a device.

FIG. 5 depicts a UV-Vis absorption spectra of an embodiment of aspin-coated di-tert-butyl7,14-dioxo-7,14-dihydroquinolino[2,3-b]acridine-5,12-dicarboxylate(TBOC-QA) thin film after annealing at 145° C. for 15 minutes.

FIG. 6 depicts a band gap determination from a Tauc plot.

FIG. 7 depicts the photocurrent density-voltage (J-V) characteristics inreverse and forward scans of embodiments of PSCs that include pristineand quinacridone coated perovskite thin films.

FIG. 8 depicts J-V curves of embodiments of PSCs.

FIG. 9 depicts J-V curves of embodiments of PSCs.

FIG. 10A, FIG. 10B, FIG. 10C, and FIG. 10D depict the statisticaldistribution of J_(SC), V_(OC), fill factor (FF), and power conversionefficiency (PCE) for embodiments of devices provided herein.

FIG. 11 depicts the incident photon conversion efficiency (IPCE) and thecorresponding integrated J_(SC) curves of embodiments of PSCs providedherein.

FIG. 12 depict Nyquist plots of embodiments of PSCs measured at a biasvoltage of 0.8 V under AM 1.5G illumination.

FIG. 13 depicts J_(SC) versus incident light intensity for embodimentsof PSCs based on embodiments of pristine and quinacridone passivatedperovskite thin films.

FIG. 14 depicts V_(OC) versus incident light intensity for embodimentsof PSCs based on embodiments of pristine and quinacridone passivatedperovskite thin films.

FIG. 15 depicts dark current-voltage (I-V) curves of embodiments ofhole-only devices (device structure: Ag/Spiro-OMeTAD/Perovskite/ITO)based on embodiments of pristine and quinacridone passivated perovskitethin films.

FIG. 16 depicts photoluminescence (PL) spectra of embodiments ofperovskite/spiro-OMeTAD samples with and without quinacridonepassivation.

FIG. 17 depicts time-resolved PL decays of embodiments ofperovskite/spiro-OMeTAD samples with and without quinacridonepassivation.

FIG. 18 depicts Fourier transform infrared (FTIR) spectra of embodimentsof quinacridone pigment, pristine, and quinacridone passivatedperovskites.

DETAILED DESCRIPTION

Provided herein are composite materials, electronic devices, and methodsof passivating surfaces. In some embodiments, the methods describedherein include a passivation strategy that uses a relatively low-costindustrial organic pigment, i.e., quinacridone, as a multifunctionalpassivation agent for halide perovskite thin films in order to achievehighly efficient and/or stable PSCs.

Methods of Passivating Surfaces

In some embodiments, the methods of passivating surfaces includeproviding a mixture that includes a liquid and a derivative ofquinacridone.

The derivative of quinacridone may be at least partially dissolved inthe liquid. In some embodiments, the derivative of quinacridone iscompletely dissolved in the liquid.

As used herein, the term “quinacridone” refers to5,12-dihydro-quino[2,3-b]acridine-7,14-dione, which has the followingstructure:

As used herein, the phrase “derivative of quinacridone” refers to acompound that (i) has a greater solubility in the liquid thanquinacridone, and (ii) is obtained by modifying the structure ofquinacridone in order to increase the solubility of the resultingderivative of quinacridone in the liquid. The structure of quinacridonemay be modified by substituting quinacridone with one or more polargroups or non-polar groups if the liquid is a polar liquid or non-polarliquid, respectively.

In some embodiments, the derivative of quinacridone is a compound of thefollowing formula:

wherein R¹ and R² are independently selected from a C₁-C₅ hydrocarbyl.

In some embodiments, the derivative of quinacridone isdi-tert-butyl-7,14-dioxo-7,14-dihydroquinolino[2,3-b]acridine-5,12-dicarboxylate:

A liquid used in the methods herein may include any liquid in which aderivative of quinacridone is at least partially soluble. The liquid maybe an organic liquid, an aqueous liquid, or a combination thereof. Insome embodiments, the liquid includes isopropanol, chlorobenzene, or acombination thereof.

A derivative of quinacridone may be present in a mixture at anyconcentration. In some embodiments, a derivative of quinacridone ispresent in a mixture at a concentration of about 0.5 mg/mL to about 5mg/mL, about 1 mg/mL to about 4 mg/mL, about 1.5 mg/mL to about 3 mg/mL,about 1.5 mg/mL to about 2.5 mg/mL, or about 1.8 mg/mL to about 2.2mg/mL.

In some embodiments, the methods of passivating surfaces includeapplying the mixture to a first surface of a film. The mixtures may beapplied to a first surface of a film using any known technique. In someembodiments, the applying of the mixture to the surface of the filmincludes spin-coating the mixture to the surface of the film.

The film to which a mixture is applied may include any one or morematerials, such as any one or more materials that may be used in anelectronic device. In some embodiments, the film includes a metal halideperovskite. In some embodiments, the film consists of a metal halideperovskite. In some embodiments, the film includes a metal halideperovskite and a matrix material. A metal halide perovskite may bedispersed in the matrix material. The matrix material may include apolymeric matrix material.

The film may include any metal halide perovskite. A metal halideperovskite may include an organic metal halide perovskite, an inorganicmetal halide perovskite, or a hybrid metal halide perovskite. In someembodiments, the metal halide perovskite is a mixed halide perovskite(i.e., a metal halide perovskite containing at least two differenthalogen atoms (e.g., Br and I)). In some embodiments, the metal halideperovskite includes methylammonium lead iodide (MAPbI₃). Othernon-limiting examples of metal halide perovskites are described in U.S.Patent Application Publication No. 2020/0270141, U.S. Patent ApplicationPublication No. 2020/019012, U.S. Patent Application Publication No.2019/0256535, U.S. Patent Application Publication No. 2019/0109291, U.S.Patent Application Publication No. 2019/0106325, U.S. Patent ApplicationPublication No. 2018/0037813, U.S. Patent Application Publication No.2017/0283693, U.S. Pat. Nos. 10,844,083, 10,774,032, 10,230,049, and10,224,459, which are incorporated herein by reference.

In some embodiments, the methods include annealing the film for a timeand a temperature effective to convert a derivative of quinacridone toquinacridone. The annealing may include any known types of annealing,such as thermal annealing or laser annealing. In some embodiments, thetime is about 5 minutes to about 40 minutes, about 10 minutes to about30 minutes, about 10 minutes to about 20 minutes, or about 14 minutes toabout 16 minutes. In some embodiments, the temperature is about 125° C.to about 175° C., about 125° C. to about 165° C., about 135° C. to about155° C., or about 140° C. to about 150° C.

Composite Materials

Composite materials also are provided herein. In some embodiments, thecomposite materials include a film that includes a metal halideperovskite. The film has a first side and a second side opposite thefirst side. The composite materials also include a coating that includesquinacridone, wherein the coating at least partially coats the firstside of the film. In some embodiments, the coating consists ofquinacridone. In some embodiments, the coating completely coats thefirst side of the film. The metal halide perovskite may include any ofthose described herein. In some embodiments, the metal halide perovskiteincludes methylammonium lead iodide (MAPbI₃).

The film that is at least partially coated with quinacridone may haveany thickness or surface area. The thickness and surface area may belimited only by the intended use of the film, such as in an electronicdevice, as described herein. In some embodiments, the film has athickness of about 450 nm to about 550 nm, about 450 nm to about 525 nm,about 460 nm to about 500 nm, or about 470 nm to about 490 nm.

Electronic Devices

Electronic devices also are provided herein. In some embodiments, theelectronic devices include an electrode, a composite material asdescribed herein, and a counter electrode. The composite material may bearranged between the electrode and the counter electrode. In someembodiments, the composite material is arranged between the electrodeand the counter electrode, and in contact with one or both of theelectrode and the counter electrode. The electrode and the counterelectrode may be an anode and a cathode, respectively, or a cathode andan anode, respectively.

The electronic devices also may include one or more other layers. Insome embodiments, the electronic devices also include one or more chargetransport layers. The one or more charge transport layers may include ahole transport layer and/or an electron transport layer. In someembodiments, the electronic devices also include one or more chargeinjection layers. The one or more charge injection layers may include ahole injection layer and/or an electron injection layer.

In some embodiments, the electronic devices also include a chargetransport layer arranged between a composite material and a counterelectrode. In some embodiments, the electronic devices also include acharge transport layer, wherein (i) the electrode contacts the secondside of the composite material, and (ii) the charge transport layercontacts the counter electrode and the coating that includesquinacridone.

The layers of the devices described herein may be formed of any suitablematerials. In some embodiments, an electrode includes indium tin oxide;a charge transport layer includes2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene(spiro-OMeTAD); a counter electrode includes gold, or a combinationthereof. One or more layers of the electronic devices, such as a chargetransport layer, may be doped. The dopant may include an n-dopant or ap-dopant.

An embodiment of a layer arrangement for an electronic device isdepicted at FIG. 1 . The layer arrangement 100 includes a substrate 110,an electrode 120, a composite material (130, 131), a charge transportlayer 140, and a counter electrode 150. The composite material isarranged between the electrode 120 and the counter electrode 150, andincludes a film 130 that includes a metal halide perovskite and acoating of quinacridone 131 that completely coats a first side of thefilm 130. The second side of the film 130 contacts the electrode 110.The charge transport layer 140 is arranged between and in contact withboth the coating of quinacridone 131 and the counter electrode 150. Thesubstrate may include any suitable material, such as glass.

The electronic devices provided herein may include a light emittingdevice, such as a light emitting diode, or a photovoltaic device, i.e.,a solar cell.

In some embodiments, the electronic device is a solar cell having astructure according FIG. 1 , wherein the electrode includes indium tinoxide, the metal halide perovskite is MAPbI₃, the charge transport layerincludes2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene(spiro-OMeTAD), and the counter electrode includes gold. Not wishing tobe bound by any particular theory, it is believed that the energy levelsof the quinacridone layer can permit cascading, directional holetransfer from the metal halide perovskite to a hole transport layer,while inhibiting electron transfer, which can increase hole extractionefficiencies and decrease charge recombination, respectively. Moreover,the strong interactions between quinacridone and the metal halideperovskite via C═O . . . Pb Lewis acid/base coordination can effectivelyreduce the surface defects of the metal halide perovskite thin film,thereby likely suppressing the trap-assisted nonradiative recombination.

In some embodiments, the solar cells described herein achieve a powerconversion efficiency of at least 20% (e.g., about 21%), withsignificantly suppressed hysteresis. Not wishing to be bound by anyparticular theory, it is believed that the hydrophobicity ofquinacridone coating layers can greatly increase the water contactangle, and improve the stability of metal halide perovskite films anddevices.

In some embodiments, the electronic device is a solar cell, and thesolar cell, after 240 hours of storage at 85° C., exhibits a powerconversion efficiency that is equal to or greater than 80%, 85%, or 90%of an initial power conversion efficiency measured prior to storage.

In some embodiments, the electronic device is a solar cell, and thesolar cell, after 1000 hours of storage at ambient conditions, exhibitsa power conversion efficiency that is equal to or greater than 90%, 92%,or 95% of an initial power conversion efficiency measured prior tostorage.

As used herein, the phrase “C₁-C₅ hydrocarbyl” generally refers toaliphatic groups containing from 1 to 5 carbon atoms. Examples ofaliphatic groups, in each instance, include, but are not limited to, analkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group,an alkynyl group, an alkadienyl group, a cyclic group, and the like, andincludes all substituted, unsubstituted, branched, and linear analogs orderivatives thereof, in each instance having from 1 to about 5 carbonatoms.

Examples of alkyl groups include, but are not limited to, methyl, ethyl,propyl, isopropyl, n-butyl, t-butyl, isobutyl, and pentyl. Example ofcycloalkyl groups include, but are not limited to, cyclopropyl,cyclobutyl, and cyclopentyl. Representative alkenyl moieties includevinyl, allyl, 1-butenyl, 2-butenyl, isobutylenyl, and 1-pentenyl.Representative alkynyl moieties include acetylenyl, propynyl, 1-butynyl,2-butynyl, 1-pentynyl, 2-pentynyl, 3-methyl-1-butynyl, and 4-pentynyl.

Unless otherwise indicated, the term “substituted,” when used todescribe a chemical structure or moiety, refers to a derivative of thatstructure or moiety wherein one or more of its hydrogen atoms issubstituted with a chemical moiety or functional group such as alcohol,alkoxy, alkanoyloxy, alkoxycarbonyl, alkenyl, alkyl (e.g., methyl),alkynyl, alkylcarbonyloxy (—OC(O)alkyl), amide (—C(O)NH-alkyl- or-alkylNHC(O)alkyl), tertiary amine (such as alkylamino, arylamino,arylalkylamino), azo, carbamoyl (—NHC(O)O-alkyl- or —OC(O)NH-alkyl),carbamyl (e.g., CONH₂, as well as CONH-alkyl, CONH-aryl, andCONH-arylalkyl), carboxyl, carboxylic acid, cyano, ester, ether (e.g.,methoxy, ethoxy), halo, haloalkyl (e.g., —CCl₃, —CF₃, —C(CF₃)₃),heteroalkyl, isocyanate, isothiocyanate, nitrile, nitro, phosphodiester,sulfide, sulfonamido (e.g., SO₂NH₂), sulfone, sulfonyl (includingalkylsulfonyl, arylsulfonyl and arylalkylsulfonyl), sulfoxide, thiol(e.g., sulfhydryl, thioether) or urea (—NHCONH-alkyl-).

In the descriptions provided herein, the terms “includes,” “is,”“containing,” “having,” and “comprises” are used in an open-endedfashion, and thus should be interpreted to mean “including, but notlimited to.” When methods, composite material, or electronic devices areclaimed or described in terms of “comprising” or “including” variouselements or features, the methods, composite materials, or electronicdevices can also “consist essentially of” or “consist of” the variouscomponents or features, unless stated otherwise.

The terms “a,” “an,” and “the” are intended to include pluralalternatives, e.g., at least one. For instance, the disclosure of “aliquid,” “a metal halide perovskite,” “a charge transport layer”, andthe like, is meant to encompass one, or mixtures or combinations of morethan one liquid, metal halide perovskite, charge transport layer, andthe like, unless otherwise specified.

Various numerical ranges may be disclosed herein. When Applicantdiscloses or claims a range of any type, Applicant's intent is todisclose or claim individually each possible number that such a rangecould reasonably encompass, including end points of the range as well asany sub-ranges and combinations of sub-ranges encompassed therein,unless otherwise specified. Moreover, numerical end points of rangesdisclosed herein are approximate. As a representative example, Applicantdiscloses that, in some embodiments, the time of annealing is about 10minutes to about 20 minutes. This disclosure should be interpreted asencompassing values of about 10 minutes and about 20 minutes, andfurther encompasses “about” each of 11 minutes, 12 minutes, 13 minutes,14, minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, and 19minutes, including any ranges and sub-ranges between any of thesevalues.

The present embodiments are illustrated herein by referring to variousembodiments, which are not to be construed in any way as imposinglimitations upon the scope thereof. On the contrary, it is to beunderstood that resort may be had to various other aspects, embodiments,modifications, and equivalents thereof which, after reading thedescription herein, may suggest themselves to one of ordinary skill inthe art without departing from the spirit of the present embodiments orthe scope of the appended claims. Thus, other aspects of the embodimentswill be apparent to those skilled in the art from consideration of thespecification and practice of the embodiments disclosed herein.

As used herein, the term “about” refers to values within ±5% or ±1% ofthe numerical value associated with the term.

EXAMPLES

The present invention is further illustrated by the following examples,which are not to be construed in any way as imposing limitations uponthe scope thereof. On the contrary, it is to be clearly understood thatresort may be had to various other aspects, embodiments, modifications,and equivalents thereof which, after reading the description herein, maysuggest themselves to one of ordinary skill in the art without departingfrom the spirit of the present invention or the scope of the appendedclaims. Thus, other aspects of this invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein.

Unless noted otherwise, the following materials were used in theExamples. Quinacridone (QA), di-(t-butyl)-dicarbonate,N,N′-dimethylaminopyridine, SnCl₂, thiourea, titanium diisopropoxidebis(acetylacetonate), CsI, methylammonium iodide (MAI), methylammoniumbromide (MABr), formamidinium iodide (FAI), PbBr₂, spiro-OMeTAD,poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA),bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI), and4-tert-butylpyridine (t-BP) were purchased from Sigma-Aldrich. PbI₂ wasbought from TCI. FK 209 Co(III) PF₆ salt was received from Xi'an PolymerLight Technology Corp. 30 N-RD TiO₂ paste was purchased from Dyesol.Clevios P VP AI 4083 type PEDOT:PSS solution was purchased from HeraeusDeutschland GmbH & Co. KG. All chemicals were used without furtherpurification.

Example 1—Synthesis of TBOC-QA

TBOC-QA was synthesized following a previously published procedure withsome minor modifications (T. L. Chen, et al. Org. Electron. 2011, 12,1126-1131).

In this example, 0.936 g QA pigment was dispersed in 150 mLtetrahydrofuran. Two equivalents of di-tent-butyl dicarbonate andN,N′-dimethylaminopyridine catalyst were added to the above solution andstirred for 24 hours at room temperature. The molecular structures of(a) TBOC-QA and (b) QA pigment were as follows:

The reaction mixtures were dried under low pressure, and the productswere purified by column chromatography using silica gel with hexane anddichloromethane as the eluents giving TBOC-QA as a yellow solid (60%yield).

Example 2—Device Fabrication

The procedure of coating halide perovskite thin films with QA used inthis example is depicted at FIG. 2 . Briefly, MAPbI₃ thin films wereprepared via a two-step sequential spin-coating processing. To permitsurface passivation of MAPbI₃ thin films via solution processing, asoluble derivative of QA, TBOC-QA, was synthesized following theprocedure of Example 1.

A solution of TBOC-QA in isopropanol/chlorobenzene (IPA/CB, 1:1, v:v)was then spin-coated onto the MAPbI₃ thin films, followed by thermalannealing at 145° C. for 15 minutes to convert TBOC-QA into QA.

The QA coated MAPbI₃ thin films were then layered with dopedspiro-OMeTAD and an Au electrode to complete the PSCs. A cross-sectionSEM image of a complete planar n-i-p PSC was collected. A schematic ofthe SEM image is depicted at FIG. 3 .

The corresponding band energy levels of the device are shown at FIG. 4 .For QA, the highest occupied molecular orbital (HOMO) energy level was−5.4 eV according to previous reports (C.-Y. Yang, et al. ACS Appl.Mater. Interfaces 2016, 8, 3714-3718), while the lowest unoccupiedmolecular orbital (LOMO) was −3.4 eV as estimated from its 2.0 eVoptical band gap (see FIG. 5 and FIG. 6 ).

As shown at FIG. 7 , the HOMO energy level of QA lied between thevalence band of MAPbI₃ and HOMO of spiro-OMeTAD, allowing the formationof a cascade energy level alignment, enabling efficient hole transportfrom MAPbI₃ to spiro-OMeTAD. The higher LOMO energy level of QA couldact as an electron blocker for the photogenerated electrons in theconduction band of MAPbI₃, effectively reducing charge carrierrecombination.

Specifically, the perovskite solar cells of this example were fabricatedbased on a planar n-i-p structure, i.e.,ITO/SnO₂/MAPbI₃/spiro-OMeTAD/Au.

The SnO₂ electron transporting layer was prepared by spin-coating SnO₂quantum dots (QDs) on an ultraviolet-ozone treated clean ITO substrate,which was then annealed at 200° C. for 1 hour. The SnO₂ QDs weresynthesized according to the procedures described in literature (Q. He,et al. J. Mater. Chem. A 2020, 8, 2039-2046).

After being cooled to room temperature and treated withultraviolet-ozone again, the substrate was transferred into a glove box.Then, a perovskite solution was spin-coated on the substrate via twoconsecutive steps of 750 rpm and 4000 rpm for 3 seconds and 20 seconds,respectively.

At the second step, 180 μL of chlorobenzene (CB) was dropped on thesubstrate before 10 seconds to end. The perovskite thin film was formedby annealing the sample on a hot plate at 145° C. for 15 minutes. TheMAPbI₃ precursor solution was prepared by dissolving MAI (1.3 M) andPbI₂ (1.3 M) in dimethylformamide/dimethyl sulfoxide (DMF/DMSO, 4:1,v:v).

To prepare the QA passivated perovskite thin film, the TBOC-QA solutionwas spin-coated on the surface of glass/ITO/SnO₂/MAPbI₃ substrate at3000 rpm for 30 seconds and annealed at 145° C. for 15 minutes. TheTBOC-QA solutions (1, 2, 4, and 8 mg mL⁻¹) were prepared by dissolvingTBOC-QA powder in a mixed solvent of isopropanol/chlorobenzene (IPA/CB,1:1, v:v).

For references, the pristine and IPA/CB treated perovskite thin filmswere also annealed under the same conditions. The hole transportinglayer was deposited by spin-casting doped spiro-OMeTAD solution at 4000rpm for 20 seconds. The solution was made by dissolving 50 mg ofspiro-OMeTAD into CB, which was then doped with Li-TFSI (10 μL, 517mg/mL in acetonitrile), t-BP (18 μL), and FK 209 Co(III) PF₆ (4 μL, 375mg/mL in acetonitrile). Finally, 80 nm thick of Au electrode wasdeposited by thermal evaporation.

The triple cationCs_(0.05)(MA_(0.17)FA_(0.83))_(0.95)Pb(I_(0.83)Br_(0.17))₃ (CsMAFA)devices based onFTO/compact-TiO₂/mesoporous-TiO₂/Cs_(0.05)(MA0.17FA_(0.83))_(0.95)Pb(I0.83Br_(0.17))₃/PTAA/Auarchitecture were fabricated according to previous report with slightmodifications (M. Saliba, et al. Chem. Mater. 2018, 30, 4193-4201).

In brief, the compact and mesoporous TiO₂ layers were deposited on cleanFTO by spin-coating a diluted titanium diisopropoxidebis(acetylacetonate) solution (1:9 by volume in ethanol) and TiO₂ paste(150 mg mL⁻¹ in ethanol), respectively. The CsMAFA thin films weredeposited by spin coating the precursor solution in a two-step protocol.For the deposition of PTAA hole transport layer, 10 mg PTAA wasdissolved in 1 mL toluene and after adding 7.5 μL Li-TFSI solution (170mg mL⁻¹ in acetonitrile) and 4 μL 4-tert-butylpyridine, the solution wasspin-coated at 3000 rpm for 30 s inside a N₂ filled glovebox. Thepassivation process was kept the same as for the MAPbI₃ system, and theconcentration of TBOC-QA solution was 2 mg mL⁻¹.

Example 3—Effect of QA Coating

The effects of QA coating on the device performance of PSCs weredetermined. By controlling the amount of TBOC-QA in the mixed IPA/CBsolvents, a concentration for achieving a relatively high PCE was foundto be 2 mg mL⁻¹ in this example. FIG. 8 depicts J-V curves of the PSCsbased on the perovskite thin films coated by QA converted from differentconcentrations of TBOC-QA solutions.

TABLE 1 Photovoltaic parameters of the PSCs based on the perovskite thinfilms coated by QA converted from different concentrations of TBOC-QAsolutions. Sample J_(SC) (mA/cm²) V_(OC) (V) FF PCE (%) QA (1 mg mL⁻¹)22.76 1.11 0.78 19.81 QA (4 mg mL⁻¹) 23.15 1.13 0.80 20.89 QA (8 mgmL⁻¹) 22.91 1.13 0.79 20.45

Photocurrent density-voltage (J-V) characteristics in reverse andforward scans of the best performing PSCs based on pristine and QAcoated MAPbI₃ thin films are shown at FIG. 7 . The device performancemetrics are summarized in Table 2.

TABLE 2 Photovoltaic parameters of the devices based on pristine and QAtreated perovskite thin films. Sample J_(SC) (mA cm⁻²) V_(OC) (V) FF PCE(%) Pristine (RS)^([a]) 22.52 1.11 0.76 18.87 Pristine (FS)^([b]) 22.511.09 0.68 16.59 QA (RS) 23.19 1.13 0.80 21.06 QA(FS) 23.17 1.11 0.7820.13 ^([a])RS: reverse scan; ^([b])FS: forward scan.

The best performing device based on pristine MAPbI₃ had a PCE of 18.87%with an open-circuit voltage (V_(oc)) of 1.11 V, a short-circuit currentdensity (J_(SC)) of 22.52 mA cm⁻², and a fill factor (FF) of 0.76. WithQA coating, the best performing device had an improved PCE of 21.06%,with an increased V_(OC) of 1.13 V, a J_(SC) of 23.19 mA cm⁻², and a FFof 0.80. To ensure that the improvement was not simply due to solventannealing by the IPA/CB used in processing of TBOC-QA layer, PSCs basedon solvent treated MAPbI₃ thin films, in the absence of TBOC-QA werealso fabricated and tested (FIG. 9 and Table 3). FIG. 9 depicts J-Vcurves of the best-performing devices (of this example) based onpristine and IPA/CB (1:1, v:v) treated perovskite thin films.

TABLE 3 Photovoltaic characteristics of the best-performing devicesbased on IPA treated perovskites. Sample J_(SC) (mA cm⁻²) V_(OC) (V) FFPCE (%) Pristine 22.52 1.11 0.76 18.87 IPA/CB 22.29 1.11 0.76 18.96

The nominal improvement in PCE of 18.96%, indicated that TBOC-QA/QAplayed a surprising role in improving the device performance. The QAcoating also surprisingly improved the hysteresis index(H=(PCE_(reverse)−PCE_(forward))/PCE_(reverse)) of PSCs (FIG. 7 )(S. Wu,et al. Joule 2020, 4, 1248-1262), with a three-fold decrease (4.5%)relative to the pristine device (12.1%). Generally, hysteresis behaviormay be caused by the mobile ions and their impact on the charge carrierextraction and recombination at the interfaces of perovskite and carriertransport layers (see, e.g., S. N. Habisreutinger, et al. ACS EnergyLett. 2018, 3, 2472-2476). The reduction of hysteresis index wasconsistent with the increased hole extraction efficiency at theperovskite/hole transport material (HTM) interfaces (see, e.g., Q. He,et al. J. Mater. Chem. A 2020, 8, 2039-2046).

In this example, more than thirty PSCs were fabricated and tested forboth pristine and QA coated MAPbI₃ thin films to probe thereproducibility, with the results shown at FIG. 10A, FIG. 10B, FIG. 10C,and FIG. 10D. The average performance characteristics of these PSCs aresummarized at Table 4.

TABLE 4 Average photovoltaic parameters of PSCs based on pristine and QAtreated perovskite layers. Sample J_(SC) (mA cm⁻²) V_(OC) (V) FF PCE (%)Pristine 22.10 1.10 0.74 17.92 QA 22.74 1.12 0.78 19.92

The devices based on pristine MAPbI₃ thin films gave an average V_(OC)of 1.10 V, a J_(SC) of 22.10 mA cm⁻², a FF of 0.74, and a PCE of 17.92%.When treated with QA, the parameters were clearly enhanced to an averageV_(OC) of 1.12 V, a J_(SC) of 22.74 mA cm⁻², a FF of 0.78, and a PCE of19.92%. All the photovoltaic parameters of PSCs were well matched withtheir best-performing results, indicating reliability of the fabricationand testing results. The incident photon conversion efficiencies (IPCEs)of the pristine and QA coated devices were also recorded and the resultsare shown in FIG. 11 . The QA coated devices exhibited better IPCEs thanthe pristine devices across the entire wavelength range (350-800 nm).

Example 4—Characterizations

To gain a further understanding of the impact of QA coating on deviceperformance, the morphological, electronic, and photophysical propertiesof QA coated MAPbI₃ thin films were characterized.

The same X-ray diffraction (XRD) patterns of pristine and QA coatedMAPbI₃ thin films suggested that a QA coating did not change thetetragonal phase of MAPbI₃. UV-Vis absorption spectra of the MAPbI₃ thinfilms also displayed little-to-no change after QA coating, implying thesame light absorption behavior of these samples.

To further characterize the effects of QA coating on the filmmorphology, SEM images of the corresponding MAPbI₃ thin films. Whileperovskite crystallites with the size of a few hundred nanometers wereclearly observed in both samples, irregularly shaped small spotsappeared after QA coating, indicating the possible formation of newspecies on the surfaces of MAPbI₃ thin films.

Atomic force microcopy (AFM) and Kelvin probe force microscopy (KPFM)measurements were performed under a nitrogen atmosphere, and the resultswere in good agreement with the observations by SEM measurement. For theQA coated sample, nanoparticles of tens of nanometers covered thesurface of MAPbI₃ thin film, further confirming surface coating by QA.The QA coated MAPbI₃ thin film also exhibited a higher surface potentialthan that of pristine MAPbI₃ thin film, which was likely attributed tothe reduction of surface defects caused by dangling bonds (N. Adhikari,et al. ACS Appl. Mater. Interfaces 2015, 7, 26445-26454). It is wellknown that the presence of these dangling bonds/defects increases therate of nonradiative recombination of photogenerated charge carriers (N.Adhikari, et al. ACS Appl. Mater. Interfaces 2015, 7, 26445-26454; andE. Aydin et al. Adv. Mater. 2019, 31, 1900428).

Thus the reduction of surface defects by the QA coating likelycontributed to the improved the photovoltaic performances shown in FIG.7 , FIG. 10A, FIG. 10B, FIG. 10C, FIG. 10D, and FIG. 11 .

Electrochemical impedance spectroscopy (EIS) was conducted to probe theresistance and charge transfer kinetics of the PSCs, and the results areshown in FIG. 12 , with fitting parameters summarized in Table 5.

TABLE 5 EIS parameters of PSCs based on different perovskite layer.Sample R_(s) (Ω) R_(ct) (Ω) R_(rec) (Ω) CPE_(ct)-T CPE_(ct)-PCPE_(rec)-T CPE_(rec)-P Pristine 18.6 79.9 489.1 3.12E−08 1.00 1.16E−081.05 QA 14.1 56.5 925.8 1.82E−09 1.19 6.67E−09 1.06

In the equivalent circuit (FIG. 13 ), the R_(s) calculated from theintersection of high frequency imaginary impedance on the X-axis is theseries resistance of a PSC, while the R_(ct) and R_(rec) ascribed to thehigh frequency and low frequency elements were the charge transportresistance and recombination resistance, respectively.

The QA coated device had a R_(s) of 14.1Ω, lower than that of thepristine device at 18.6Ω, which suggested more efficient charge transferin the device. HOMO energy of QA was appropriate to form a cascade withMAPbI₃ and spiro-OMeTAD, resulting in the improvement of FF from 0.76 to0.80, as shown in FIG. 4 . The smaller R_(ct) (56.5Ω) and larger R_(rec)(925.8Ω) of the QA coated device, as compared to those of the pristinedevice with values of 79.9Ω and 489.1Ω, suggested more efficient holeextraction and suppressed charge recombination at the interfaces.

Light intensity dependent J_(SC) and V_(OC) measurements were thenperformed to ascertain the charge recombination kinetics of the PSCs.From a linear fit of the J_(SC) versus intensity data (FIG. 13 ), the QAcoating shows a greater slope (0.99) than that of the pristine device(0.96), signifying the enhanced charge extraction in the former likelydue to decreased trap density at the passivated interfaces. The V_(OC)versus light intensity is depicted in FIG. 14 . The ideality factor (n)can be calculated from the V_(OC) and light intensity (P_(light)) usingthe equation (1):

$\begin{matrix}{n = {\frac{q}{k_{B}T}\frac{{dV}_{OC}}{{d\ln}( P_{light} )}}} & (1)\end{matrix}$where k_(B) is the Boltzmann constant, q is elementary charge of theelectron, and the n is representative of the charge carrierrecombination process. In general, if the n value approaches unity, thedevice performance likely is dominated by bimolecular recombination,i.e. the recombination of free electrons and holes in the perovskitelayer. When n approaches 2, the trap-assisted Shockley-Read-Hall (SRH)charge carrier recombination likely is dominant.

Next, n values of 1.96 and 1.45 for the pristine and QA coated devices,respectively were determined, which indicated that a trap-assisted SRHrecombination process was occurring at the charge collection interfaces.The decreased n value for the device with QA coating likely suggestedthe suppression of trap-assisted SRH recombination due to reducedtrap-state density, which manifested in the increased FF and PCE (FIG.10A-FIG. 10D).

The reduction of trap-state density in QA coated perovskite thin filmswas also confirmed by the quantitative characterization of hole-onlydevices via a space-charge-limited current (SCLC) method (FIG. 15 ). Atthe region of low bias voltage, the linear relation indicated an ohmicresponse of the device, while the current increased quickly as thevoltage went up and exceeded the kink point, signifying the trap-stateswere likely fully filled. The trap-state density (n_(t)) could becalculated from the trap-filled limit voltage (V_(TFL)) using theequation (2):

$\begin{matrix}{n_{t} = \frac{2\varepsilon\varepsilon_{0}V_{TFL}}{eL^{2}}} & (2)\end{matrix}$wherein ε represents the relative dielectric constant of perovskite(ε=28.8 for MAPbI₃), ε₀ is the vacuum permittivity, and L is thethickness of the perovskite layer.

From the cross-section SEM image (FIG. 3 ) the perovskite thickness wasdetermined to be ˜480 nm. As shown in FIG. 15 , the VTFL of pristine andQA coated thin films were 0.39 and 0.26 V giving n_(t) values of5.39×10¹⁵ and 3.60×10¹⁵ cm⁻³, respectively. The lower value for thedevice with QA coating again supported the conclusion that the holetrap-state density of perovskite thin films was greatly reduced by QApassivation, resulting in lower charge recombination and increased fillfactor, as shown in FIG. 10A-FIG. 10D.

To further probe the effect of QA coating on the charge transferdynamics between perovskite layer and HTM, steady-statephotoluminescence (PL) and time-resolved PL (TRPL) spectra were recordedfor glass/perovskite/HTM devices. The QA coated MAPbI₃ thin filmexhibited stronger PL quenching (FIG. 16 ) and decreased excited statelifetime of 8.8 ns (FIG. 17, Table 6) relative to the pristine film(13.8 ns). This emission quenching was consistent with more rapid andefficient hole extraction at the perovskite/HTM interfaces and theincreased FF and reduced hysteresis index.

TABLE 6 Fitted parameters for time resolved PL decay of devices based ondifferent perovskite films (architecture: glass/perovskite/spiro-OMeTAD). A biexponential decay model was used. Sample τ₁ (ns) τ₂ (ns) A₁(%) A₂ (%) τ_(ave) (ns) Pristine 3.8 26.2 89.5 10.5 13.8 QA 3.2 22.794.6 5.4 8.8

Flourier transform infrared (FTIR) spectra were recorded to gain abetter understanding of the interactions between QA coating and theMAPbI₃ thin film underneath, with results shown at FIG. 18 . Incomparison to the pristine film, several new absorption features wereobserved for the QA treated MAPbI₃ thin films (dotted oval of FIG. 18 )that were consistent with the presence of QA. The characteristicstretching vibration of the C═O in QA shifted from 1625 cm⁻¹ to ˜1616cm⁻¹ upon deposition on the MAPbI₃ thin film. This shift could have beenthe result of a O . . . Pb coordination bonding via Lewis base-acidinteraction between the C═O bond of QA and Pb²⁺ in the MAPbI₃ thin film.The FTIR spectra for PbI₂ and QA treated PbI₂ were recorded to furtherverify this hypothesis. It was found that the shift of the C═O vibrationin QA treated PbI₂ followed the same trend as that of QA coated MAPbI₃thin films. These results confirmed that QA interacted with the MAPbI₃though Lewis base-acid coordination between C═O and Pb²⁺. The carbonylstretch for the ester groups of TBOC-QA at ˜1744 cm⁻¹ disappeared afterannealing, indicating the complete conversion of TBOC-QA into QA.

X-ray photoelectron spectroscopy (XPS) was conducted to further explorethe nature of interactions between QA and MAPbI₃. Increased relativepeak intensities and newly appeared peaks of C 1 s and O 1 s core levelsfor the QA coated sample confirmed the presence of QA on the MAPbI₃surface. High-resolution XPS spectra of the pristine MAPbI₃ thin filmshowed two peaks located at 137.9 and 142.8 eV, corresponding to the Pb4f 7/2 and Pb 4f 5/2 core levels, respectively. Two additional peaks at136.3 and 141.2 eV were assigned to metallic Pb) (Pb⁰) sites presumablydue to evaporation of I⁻ ions and formation of under-coordinated Pb²⁺sites during thermal treatment. The Pb⁰ defects could act asrecombination centers that hindered the photovoltaic performance ofPSCs. With QA coating on MAPbI₃ thin films, the Pb⁰ peaks disappeared,suggesting the QA coating on MAPbI₃ thin films not only restricted theevaporation of iodide but also passivated the of Pb⁰ defects via thestrong interactions between QA and MAPbI₃.

To better understand the interactions between QA and MAPbI₃, densityfunctional theory (DFT) calculations were performed. In thecalculations, a PbI₂ terminated symmetric slab was constructed from thepartially relaxed tetragonal MAPbI₃. The slab consisted of 2×2periodicity in the a-b plane and three layers of PbI₂ layers in the caxis. A 4×4×1 k-point mesh was adopted for Brillouin-zone sampling.Afterward, the QA molecule was placed on the (001) PbI₂ terminatedperovskite surface orthogonally.

The optimized difference charge density distribution of QA and MAPbI₃were graphically recorded. In agreement with the FTIR results (FIG. 18), the O atom of C═O group in QA was anchored to the exposed Pb atomwith bond length of 3.04 Å. Moreover, the characteristics of electronloss were observed on H atoms of benzyl group close to MAPbI₃ surfaceindicating the Coulomb interaction between H and I. This interactioncould have helped suppress the evaporation of iodine in MAPbI₃ duringannealing process. The interaction energy between the QA molecule andthe perovskite surface was calculated as:E_(interactions)=E_(perovskite-molecule)−E_(perovskite)−E_(molecule),and the value was found to be as high as −3.29 eV. As could be inferredfrom the charge density difference isosurface, the C═O group on the QAmolecule strongly interacted with the Pb²⁺ on the perovskite surface.

To evaluate the universality of this passivation strategy, PSCs based ontriple cation Cs_(0.05)(MA_(0.17)FA_(0.83))_(0.95)Pb(I_(0.83)Br_(0.17))₃(CsMAFA) perovskite thin films were fabricated and tested. The J-Vcharacteristics of the best performing PSCs based on pristine and QAcoated CsMAFA thin films were plotted, and the corresponding deviceperformance metrics are summarized in Table 7.

TABLE 7 Photovoltaic characteristics of the best-performing devicesbased on pristine and QA coated CsMAFA thin films. Sample J_(SC) (mAcm⁻²) V_(OC) (V) FF PCE (%) Pristine 22.63 1.10 0.77 19.36 QA 23.21 1.140.80 21.17

The pristine device based on CsMAFA thin film had a PCE of 19.36% withan V_(oc) of 1.10 V, a J_(SC) of 22.63 mA cm⁻², and a FF of 0.77. WithQA coating, an improved PCE of 21.17%, with an increased V_(OC) of 1.14V, a J_(SC) of 23.21 mA cm⁻², and a FF of 0.80, were achieved. Thisresult suggested that this QA passivation strategy could be extended toother type of perovskite systems for efficient and stable PSCs.

Besides surface passivation, the hydrophobicity and insolubility of theQA layer benefited the stability of QA coated perovskite thin films.Static contact angle measurements were performed to evaluate the surfacehydrophobicity of the perovskite thin films. The pristine MAPbI₃ thinfilm showed a contact angle of 35.6°, which was significantly increasedto 77.2° after QA coating. The water infiltration and diffusioncharacteristics of perovskite thin films were then examined by comparingthe diffusion area of water droplet. It was observed that a waterdroplet on a pristine MAPbI₃ thin film diffused to about 10 mm in 15seconds, while a similar drop on a QA passivated MAPbI₃ thin filmretained its initial size even after 20 minutes.

Thus, the QA passivated film exhibited lower moisture infiltration anddiffusion rates. It was anticipated that the hydrophobicity and slowedinfiltration/diffusion rates of the QA layer would inhibit moistureattack of the perovskite layer. XRD patterns of pristine and QApassivated perovskite thin films before and after exposure to ambientconditions, respectively were collected. After exposure for one month,the pristine sample discolored and scaled from the substrate, and theformation of PbI₂ and MAPbI₃·H₂O was observed, likely due to thedecomposition and hydration of MAPbI₃. In contrast, the QA coated MAPbI₃thin film displayed impressive stability with little-to-no change of thecolor and phase after storage in ambient conditions for one month.

To investigate the effects of QA coating on the device stability, thechange of PCEs was examined for the pristine and QA passivated MAPbI₃thin films under long-term storage and continuous illumination inambient conditions. The device based on pristine MAPbI₃ showed asignificant reduction of PCEs with 80.4% performance loss after storingin 50-60% relative humidity (RH) at room temperature for 1000 hours.

In comparison, the device with QA coating retained 89.7% of its initialPCE with only a 10.3% reduction in performance over 1000 hours. Undercontinuous illumination, the unencapsulated device with QA coatingretained 85.5% of its initial PCE after exposure to AM 1.5G for 48hours. In contrast, the pristine MAPbI₃ device exhibited a much fasterdecline in performance to 21.2% of its initial PCE. These resultsstrongly indicated that the hydrophobic and insoluble QA layer served asa protective coating against degradation of the perovskite layer bymoisture.

The high temperature stability of the devices stored in a N₂ environmentat 85° C. were also measured. The spiro-OMeTAD HTM was replaced bypolytriarylamine (PTAA), considering that the mobility of lithium iondopants would lead to quick device degradation when the temperature goesover 50° C. for thermal stability testing. The J-V curves andcorresponding photovoltaic parameters of the PSCs with PTAA HTM werecollected, and the results are depicted at Table 8.

TABLE 8 Photovoltaic characteristics of the best- performing devicesbased on PTAA HTL. Sample J_(SC) (mA cm⁻²) V_(OC) (V) FF PCE (%)Pristine 22.25 1.10 0.76 18.63 QA 23.05 1.13 0.80 20.91

The pristine and passivated devices showed a PCE of 18.63% and 20.91%,respectively. The QA passivated device maintained 85.7% of its initialPCE after 240 hours of storage at 85° C., which was significantly betterthan that of pristine MAPbI₃ device (44.3%).

UV-Vis absorption spectra of perovskite thin films were measured on CARY5000 UV-Vis NIR spectrophotometer (Agilent Technologies). X-Raydiffraction spectra were recorded by SmartLab X-ray diffractometer(Rigaku Corporation) with Cu Kα radiation. Scanning electron microscopyimages were captured by Nova NanoSEM 400 (FEI Company) at 3.0 KVscanning voltage. Atomic force microscope and Kelvin probe forcemicroscopy measurements were performed on surface of perovskite thinfilms in ambient conditions using Icon scanning probe microscope (BrukerCorporation) in a single-pass frequency modulated (FM-KPFM) mode.

The contact angles of perovskite thin films with water drops weremeasured by CAM 200 optical tensiometer (KSV Instruments). Fouriertransform infrared (FTIR) spectra were recorded by FT/IR-6800 FTIRSpectrometer (JASCO International Co., Ltd.). X-ray photoelectronspectroscopy (XPS) was conducted using a PHI 5000 series XPS with Kαradiation of Al. Charge compensation was performed using adventitious C1s peak (284.6 eV). Spectra background were fitted and subtracted usingan integrated Shirley function. XPS curves were deconvoluted using aVoight peak function for metal core electron spectra and gaussian peakfunctions for the rest.

Steady-state photoluminescence measurements of perovskite films withoutand with HTL were performed on FS5 spectrofluorometer (EdinburghInstruments). The corresponding time-resolved PL curves were recorded bythe same instrument which equipped a 450 nm laser (EPL-450, EdinburghInstruments). The carrier lifetimes were fitted with a biexponentialfunction y=A₁×exp(−x/τ₁)+A₂×exp(−x/τ₂)+y₀. The weighted averagelifetimes were calculated by <τ>=ΣAiτi²/ΣAiτi. The currentdensity-voltage characteristics of perovskite solar cells were takenusing the IV5 Solar Cell I-V Measurement System (PV Measurements, Inc.).The electrochemical impedance spectroscopy measurement was carried outon a Gamry Interface 1000E potentiostat under AM 1.5G illumination inthe frequency range from 10 Hz to 1 MHz with an alternative signalamplitude of 10 mV, in which the potential bias was fixed at 0.8 V. Allthe devices were covered by a mask with the active area of ˜0.15 cm² andmeasured under the illumination of AM 1.5G in ambient condition. Theincident photon-to-electron conversion efficiency (IPCE) measurement wascarried out by using QEX10 (PV Measurements, Inc.).

Example 5—DFT Calculations

A PbI₂ terminated symmetric slab was constructed from the partiallyrelaxed tetragonal MAPbI₃ reported in the literature (K. Frohna, et al.Nat. Commun. 2018, 9, 1829).

The slab consisted of 2×2 periodicity in the a-b plane and three layersof PbI₂ layers in the c axis separated by 20 A of vacuum. Firstprinciples calculations were carried out using the quantum espressopackage (P. Giannozzi, et al. J. Phys.: Condens. Matter 2009, 21,395502).

The revised Perdew-Burke-Ernzerh of generalized gradient approximation(PBEsol) was used for exchange-correlation along with Grimme's DFT-D3Van der Waals correction (J. P. Perdew et al. Phys. Rev. Lett. 1996, 77,3865-3868; J. P. Perdew et al. Phys. Rev. Lett. 2008, 100, 136406; S.Grimme, et al. J. Chem. Phys. 2010, 132, 154104; S. Grimme, J. Comput.Chem. 2006, 27, 1787-1799; and P. E. Blochl, et al. Phys. Rev. B 1994,49, 16223-16233).

The ion cores were described using projector-augmented wave (PAW)psuedopotentials (P. E. Blochl, et al. Phys. Rev. B 1994, 49,16223-16233). The plane-wave expansion cutoff was set at 22 Ry andcharge density cutoff at 88 Ry. Atomic positions were relaxed using aforce conversion threshold of 1×10⁻³ Ry/bohr. Only surface atoms wereallowed to relax to reduce computational cost. A 4×4×1 k-point mesh wasadopted for Brillouin-zone sampling. The interaction energy between theQA molecule and the perovskite surface was calculated as:E _(interactions) =E _(perovskite-molecule) −E _(perovskite) −E_(molecule)

The invention claimed is:
 1. A method of passivating a surface, themethod comprising: providing a mixture comprising a liquid and aderivative of quinacridone, wherein the derivative of quinacridone is atleast partially dissolved in the liquid; applying the mixture to a firstsurface of a film, wherein the film comprises a metal halide perovskite;and annealing the film for a time and a temperature effective to convertthe derivative of quinacridone to quinacridone.
 2. The method of claim1, wherein the derivative of quinacridone is a compound of the followingformula:

wherein R¹ and R² are independently selected from a C₁-C₅ hydrocarbyl.3. The method of claim 1, wherein the derivative of quinacridone isdi-tert-butyl-7,14-dioxo-7,14-dihydroquinolino[2,3-b]acridine-5,12-dicarboxylate,which has the following structure:


4. The method of claim 1, wherein the applying of the mixture to thesurface of the film comprises spin-coating the mixture to the surface ofthe film.
 5. The method of claim 1, wherein the metal halide perovskitecomprises methylammonium lead iodide (MAPbI₃).
 6. The method of claim 1,wherein the liquid comprises isopropanol, chlorobenzene, or acombination thereof.
 7. The method of claim 1, wherein a concentrationof the derivative of quinacridone in the mixture is about 1.5 mg/mL toabout 2.5 mg/mL.
 8. The method of claim 1, wherein the time is about 10minutes to about 20 minutes, and the temperature is about 135° C. toabout 155° C.